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Pressure-induced insulator–conductor transition in a photoconducting organic liquid-crystal film

Nature volume 418, pages 162–164 (2002)Cite this article

Abstract

Intermolecular separation determines the extent of orbital overlap and thus the rate of electron transfer between neighbouring molecules in an organic crystal. If such a crystal is compressed, the resistivity decreases owing to a diminishing intermolecular distance1. Metal–insulator transitions have been observed by applying hydrostatic pressure to, for example, Langmuir films of metal nanoparticles2,3. But previous attempts to observe a clear transition point in organic crystals, such as anthracene and tetracene, were not successful owing to difficulties with electrically insulating the high-pressure cell4. Here we report a different approach by using a sample that is photoconductive and forms an organized film. A cylindrical tip (∼100 μm in diameter) was used to compress the sample instead of a piston/cylinder structure, entirely eliminating the problem of electrical insulation. Furthermore, by illuminating the sample with a laser, the conductivity of the sample is increased by several orders of magnitude. By monitoring the photocurrent with sensitivity at the 10-13 A level, changes in resistivity at very low pressure could be monitored. We observe a sharp increase in current that could indicate a transition from hopping to delocalized conduction.

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Figure 1: Schematic diagram of the experimental apparatus. A PZT pusher capable of moving extremely slowly (a few Å s-1) was used to drive the tip so that the sample could be maintained in a quasi-equilibrium state during compression.
Figure 2: Photocurrent as a function of compression and expansion of a ZnODEP film about 6 μm thick between ITO glass and a stainless-steel tip.
Figure 3: Photocurrent as a function of distance during the compression of a ZnODEP film about 10 μm thick between ITO glass and a stainless-steel tip.
Figure 4: Current as a function of bias voltage in ZnODEP semiconductor (pressure about 2.7 kbar).

References

  1. Drickamer, H. G. & Frank, C. W. Electronic structure, electronic transitions, and the high pressure chemistry and physics of solids. Annu. Rev. Phys. Chem. 23, 39–64 (1972)

    Article  ADS  CAS  Google Scholar 

  2. Collier, C. P., Saykally, R. J., Shiang, J. J., Henrichs, S. E. & Heath, J. R. Reversible tuning of silver quantum dot monolayers through the metal-insulator transition. Science 277, 1978–1981 (1997)

    Article  CAS  Google Scholar 

  3. Henrichs, S., Collier, C. P., Saykally, R. J., Shen, Y. R. & Heath, J. R. The dielectric function of silver nanoparticle Langmuir monolayers compressed through the metal insulator transition. J. Am. Chem. Soc. 122, 4077–4083 (2000)

    Article  CAS  Google Scholar 

  4. Samara, G. A. & Drickamer, H. G. Effect of pressure on the resistance of fused-ring aromatic compounds. J. Chem. Phys. 37, 474–479 (1962)

    Article  ADS  CAS  Google Scholar 

  5. Liu, C.-Y., Pan, H.-L., Tang, H., Fox, M. A. & Bard, A. J. Effect of structural order on the dark and photocurrents in zinc octakis (β-decoxyethyl)porphyrin thin-layer cells. J. Phys. Chem. 99, 7632–7636 (1995)

    Article  CAS  Google Scholar 

  6. Schouten, P. G., Warman, J. M., de Haaas, M. P., Fox, M. A. & Pan, H-L. Charge migration in supramolecular stacks of peripherally substituted porphyrins. Nature 353, 736–737 (1991)

    Article  ADS  CAS  Google Scholar 

  7. Liu, C.-Y. & Bard, A. J. Optoelectronic properties and memories based on organic single-crystal thin films. Acc. Chem. Res. 32, 235–245 (1999)

    Article  CAS  Google Scholar 

  8. Liu, C.-Y. & Bard, A. J. in Conjugated Oligomers, Polymers, and Dendrimers: From Polyacetylene to DNA (ed. Brédas, J.-L.) 85–116 (De Boeck Université, Paris, 1999)

    Google Scholar 

  9. Gregg, B. A., Fox, M. A. & Bard, A. J. Photovoltaic effect in symmetrical cells of a liquid crystal porphyrin. J. Phys. Chem. 94, 1586–1598 (1990)

    Article  CAS  Google Scholar 

  10. Liu, C.-Y. & Bard, A. J. Optoelectric charge trapping/detrapping in thin solid films of organic azo dyes: Application of scanning tunneling microscopic tip contact to photoconductive films for data storage. Chem. Mater. 10, 840–846 (1998)

    Article  CAS  Google Scholar 

  11. Liu, C.-Y., Pan, H.-L., Fox, M. A. & Bard, A. J. Reversible charge trapping/detrapping in a photoconductive insulator of liquid crystal zinc porphyrin. Chem. Mater. 9, 1422–1429 (1997)

    Article  CAS  Google Scholar 

  12. Aust, R. B., Bentley, W. H. & Drickamer, H. G. Behavior of fused-ring aromatic hydrocarbons at very high pressure. J. Chem. Phys. 41, 1856 (1964)

    Article  ADS  CAS  Google Scholar 

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Acknowledgements

We thank F.-R.F. Fan for discussions. This work was supported by the National Science Foundation and the Robert A. Welch Foundation.

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  1. Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas, 78712, USA

    Chong-yang Liu & Allen J. Bard

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  1. Chong-yang Liu
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Correspondence to Allen J. Bard.

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Liu, Cy., Bard, A. Pressure-induced insulator–conductor transition in a photoconducting organic liquid-crystal film. Nature 418, 162–164 (2002). https://doi.org/10.1038/nature00875

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